Variable inductor having an internally wound coil of melical form



3,2462 68 WOUND April 12, 1966 H. F. SHEPHERD. JR

VARIABLE INDUCTOR HAVING AN INTERNALLY COIL OF HELICAL FORM 2 Sheets-Sheet 1 Filed Sept. 5, 1965 Haw/Q0 A 56 5 /9590, JP.

INVENTOR.

KEA/DlQ/C'K 0/70 STOAZV BY Z 2 ATTOE/VEKS' Aprifi 12, 1966 H. F. SHEPHERD, JR 3,245,268

VARIABLE INDU R HAVING AN INTERNALLY WOUND C OF HELICAL FORM Filed Sept. 5, 19645 2 Sheets-Sheet 2 United States Patent 3,246,268 VARIABLE INDUCTOR HAVING AN IN TERNALLY WGUND COIL 0F HELICAL FORM Howard F. Shepherd, In, 127 S. Citrus, Los Angeles, Calif. Filed Sept. 3, 1963, Ser. No. 306,240 11 Claims. (Cl. 336-15) This invention relates to devices for use in electrical circuits, and more particularly to a precision variable impedance.

Although the device of the present invention will have a larger scope of application than that disclosed herein, and the invention should not be limited to this disclosure for this reason, the invention has been found to be especially useful as a precision variable inductor. However, variable resistors and variable capacitors and sequential commutator type switching devices may also be construed in accordance with the present invention.

In many applications, it is desired that variable inductors be constructed in a manner such that they are mechanically rugged. In these cases, it is required that they operate eiiiciently while they are being subjected to vibrations of a large magnitude and high acceleration loads. Variable inductors of the prior art have had a construction including a coil of wire wound external to a form. The tenuous character of such partially supported turns of a wire coil is well known.

Prior art variable inductors, in general, have suffered from the disadvantages that they are unreliable. That is, it is difiicult to obtain the same electrical characteristic from such an inductor for a mechanical setting when the setting has been changed and thereafter returned to the original setting.

Another disadvantage of variable inductors of the prior art has been the relatively high torque which has been required to adjust the inductance of such circuit elements.

In accordance with the present invention, the abovedescribed and other disadvantages of the prior art are overcome by providing a variable impedance including a first body having an approximately cylindrical hole therein. The surface defining the hole is provided with a helical groove in it. A second body having helical male screw threads is then disposed in the groove. The second body is provided with a passageway along its length, the axis of said passageway forming a helix. A conductive wire is then located in a position with one end starting in the groove of the first body, extending through the second body passageway, and returning to the groove in the first body. The first body groove is provided with a conductive surface contiguous to only a portion of the conductive wire, at least a portion of the surface of the first body groove being made of an insulating material. Means are also provided to rotate the second body in the first body groove.

In accordance with the present invention, a conductive wire is laid in a groove of an insulator so that the same is held rigid therein. This means that a variable inductor made in accordance with the present invention may be subjected to extreme shock and vibration and, even though such an inductor is so subjected, the helical characteristics of the inductor will not be temporarily or permanently effected. Further, due to the fact that the turns of wire are held rigidly in the insulator grooves, it is possible to reset a variable inductor constructed in accordance with the present invention to the same mechanical position at a successive series of times during its use, and the variable inductor will invariably produce the same electrical characteristics.

In accordance with an outstanding feature of the present invention, the variable inductor is made in a manner 3,246,268 Patented Apr. 12, 1966 such that the unstressed diameter of the conductive wire helix is greater than the inside diameter of the insulator groove. This makes it possible to hold the conductive wire in tension in the groove and thus keep it rigid in the groove.

It is also another outstanding feature of the present invention that the second body referred to above is a low bearing friction insulator, such as a Teflon body or a nylon body. For this reason, the internal or second body is easily slidable on the wire. The variable inductor of the present invention may thus be adjusted with the use of very little torque, even though the inductor will serve its purpose under extreme conditions of shock and vibration. The combination of both the wire and groove arrangement with a Teflon or nylon passageway is thus also an outstanding feature of the present invention.

Still another feature of the invention resides in the use of an insulator groove square in cross section. It has been found that mechanical movement of the conductive wire into and out of such a groove is facilitated by this construction. The quality of an inductor constructed in this manner is also higher for this reason.

It is another advantage of the present invention that the variation in inductance produced by rotation of the internal or second body does not increase the diameter of the conductive wire helix. This also makes it possible to use very excellent conductors. For example, a silver plated wire may be used. This is made possible due to the fact that little or no wire deformation is produced and because no metal to metal frictional engagement is relied upon for metal contact. The primary change in metal to metal contact takes place when the helical wire in effect rolls on at metal internal surfaces of the first body in the helical groove in it. Although as just explained, the variable inductor of the present invention relies upon a metal to metal contact within the conductive portion of the first body and the retention of the wire in the nonconductive portion of the first body, it will be appreciated that the variable resistor, variable capacitor and sequential switching devices will not necessarily involve the same contact depending upon the characteristic of the circuit element and the electrical characteristics desired.

It is also an outstanding feature of the present invention that the same is, in effect, self contained. That is, it is relatively small in size and has no moving parts external of the helical coil of wire. For this additional reason, it may be manufactured as a sealed unit.

The above-described and other advantages of the present invention will be better understood from the following description when considered in connection with the accompanying drawings.

In the drawings which are to be regarded as merely illustrative FIG. 1 is a perspective view, partly in section, of a variable inductor constructed in accordance with the present invention;

FIG. 2 is a longitudinal sectional view of the inductor shown in FIG. 1;

FIG. 3 is a transverse sectional view of the inductor taken on the line 33 shown in FIG. 2; and

FIG. 4 is an enlarged longitudinal sectional view of the upper right hand corner of the view shown in FIG. 2.

In FIG. 1, a variable induct-or 10 having threaded output terminal posts or bolts 11 and 12 is shown between which a solid helical wire 13 is connected, wire 13 being made of a spring metal and having a circular cross section.

The principal body portion of inductor 10 includes a cylinder 14 made of an insulation material and a cylinder 3 located in a bore 16 of cylinder .14, cylinder 15 being made of a conductive metal.

Post 11 projects through .both cylinders 14 and '15 and is maintained in that position by a nut 17 threaded to post 11. As shown in FIG. 2, post 11 is, in actuality, a bolt having a head 18 and a shank 19. A terminal connectorZO, soldered or welded to one end of wire 13 is held in a fixed position between bolt head '18 and the internal surface of cylinder 15.

As can be seen from FIGS. 1, 2 and 4, post 12 similarl'yholds a terminal connector 21 in a similar position relative to cylinder 14. Connector 21 is likewise soldered or welded to-the right end of wire '13. A nut 17 holds post 12 in position through cylinder 14.

A helical groove runs throughout the entire length of cylinder 14. This groove is indicated at 22 in the internal wall of cylinder 14 at the right end thereof. The same groove is also indicated at 23 in the internal wall of cylinder 15. Even though cylinders 14 and 15 are made of two different materials, the grooves 12 and 23 mate precisely at the termination 24 of cylinder 15 at its right end.

The groove at 22 and 23 serves two purposes. Wire 13 rests firmly in this groove in a position spaced to the left from the left end of an intermediate body 25 and in a position spaced from the right of the right end of body 25. Further, body 25 is provided with a ring 2e fixed with it which has a helical male screw thread 27 with a pitch identical to that of the groove. The thread 27 in fact mates with and is engaged with the groove at 22 and 26.

A better understanding of the operation of the inductor 10 may be obtained by noting, at this point, that all the structure of the inductor may be made of an insulation material with the exception of posts 12, nut 17 and 17,'wire' 13, connectors and 21, and cylinder 15. Further, it is an advantage of the device of the present invention that a low friction insulating material is used for one and preferably several or all of the insulation materials of inductor 10. For example, polymerized tetrafiuoroethylene or Teflon may serve this purpose.

Intermediate body turns on a shaft 28 which has a pinttle- 29 fixed to its left end and a pintle 30 fixed to its right end. Pintle 29 is rotatable in a bore 31 of a disc 32' that closes the left end of cylinder 14. Pintle 30 is rotatable in a bore 33 of a disc 34 that closes the right end of cylinder 14. Discs 32 and 34 are held in fixed positions relative to cylinder 14. Disc 32 has a projection 35 which fits inside cylinder 15. Similarly, disc 34 has a projection 36 that fits inside cylinder 14. Shaft 28 has a key 37 that is fixed relative to it.

Body 25 is provided with a cylinder 38 which has a bore 39 through which shaft 28 projects. Cylinder 38 also has a keyway 40 through which key 37 projects. Body 27 is slidable on shaft 28 and key 37. Cylinder 38 has a helical body 41 fixed to it. The helical body is provided with a helical passageway 42 through which wire 13 extends.

A knob 43 is fixed to right pintle 30 to turn shaft 28 and key 37. When shaft 28 and key 37 are turned, the entire structure of body 25 inside cylinders 14 and 15 turn and move lengthwise on shaft 28 and key 37. When this motion is produced, wire 13 is withdrawn from the groove at 22 and 23 at one end of body 41 and is laid into the groove at the other end of body 41 simultaneously.

Note will be taken from FIG. 2 that passageway 42 has a circular cross section.

The shape of passageway 42 has heretofore been described as helical. The shape of this passageway is, in fact, approximately helical. Its curvature at the very ends of body 41 is, in fact, circular as can be seen from FIG. 1 and from the shape of wire 13 therein at FIG. 2.

Although certain parts of body 25- have been described as separate parts, all of these parts may in fact be made 4 in one integral molding operation as suggested by some of the sections in the drawings.

Note will be taken that to an extent, body 41 and ring 26 have a common construction at the position of passageway 42 indicated at 42' in \FIG. 2.

As stated previously, the groove at 22 and 23 in cylinders 14 and 15 mate precisely. This means that a male thread '27 on ring 26 can be turned from a position entirely within cylinder 14 outside of cylinder 15 to a position entirely within cylinder 15.

Note will be taken, and it is a feature of the invention, that the cross section of the groove at 22 and 23 is square as shown in FIG. 4.

The inductance from post 11 to post 12 is changed by rotating knob 43 and the structure fixed with it. This rotates disc 26 in the groove at 22 and 23 and moves body 25 lengthwise in cylinders 14 and 15. All the turns of wire 13 that lie in contact with cylinder 15 are shorted out. This means that the inductance between posts 11 and 12 is determined by the longitudinal position of body 25 inside cylinders 14 and 15, and precisely the point that wire 13 leaves cyinder 15 and enters passageway 42 at the left hand end of body 41, shown in FIGS. 1 and 2.

The inductance between posts 11 and 12 will then be determined by the length of wire 13 between the left end of body 41 and post 12, as shown in FIGS. 1 and 2.

From the foregoing, it will be appreciated that the inductor 10 of the present invention is extremely rugged. Although by their very nature, the turns of wire 13 are relatively unstable and susceptible to electrical and mechanical change when they are subjected to high acceleration loads and vibration forces, the nature of the turns of wire/13 and the surrounding and stabilizing characteristic of the groove at 22 and 23 make any substantial movement of the turns of wire 13 impossible. Further, knob 43 may be turned from one position to another and then returned to the initial position and the reliability of the inductor 10will be such that the inductances thereof for the initial and final settings of knob 43 will be identical.

It is an outstanding feature of the present invention that inductor lit is made by winding wire 13 on a mandrel having a cylindrical external surface of an outside diameter greater than the inside diameter of the helix of wire 13 after it has been laid in the groove at 22 and 23. This makes it possible to hold wire 13 in tension in the groove and keep it in a rigid and immovable position, but for its movement through passageway 42 in body 41.

It is also an outstanding feature of the present invention that body 41 and especially the surface of passage- Way 42 is made of a low bearing friction insulator such as Teflon. It is striking to note that even though Wire 13 is put through some temporary deformation in passing through body 41, the deformation is not permanent and body 41 does in fact slide very easily over Wire 13 when appropriate low friction insulating materials are employed in the construction of body 41. Thus, although the reasons for the same are not easily understood, the inductor retains an extremely high degree of rigidity whereas knob 43 may be turned and the inductance of the inductor 10- changed by the application of a relatively small torque to shaft 28.

It is another advantage of the invention that the sameis in effect self-contained. That is, little or'no need. exists for structure on the exterior of cylinder 14 and discs 32 and 34.

Although only one specific embodiment of the present invention has been described and illustrated herein, many changes and modifications Will of course suggest themselves to those skilled in the art. This single embodiment has been selected for this disclosure for the purpose of illustration only. The present invention should therefore not be limited to the embodiment so selected, the true scope of the invention being defined only in the appended claims.

What is claimed is:

1. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein; a flexible conductor having spaced portions in spaced portions of said groove at each end of said groove, the internal surface at one end of said hole having a conductivity less than that of said conductor; a metal body positioned contiguous to said conductor at least at one point along the length thereof; and a second body in said first body hole, said second body having a passageway therethrough to surround said conductor, said passageway extending from one of said spaced portions of said first body groove to the other spaced portion thereof, said passageway following the shape of a helix of a diameter smaller than said first body groove and a pitch different from that of said groove, said conductor extending through said second body passageway, said second body passageway being slidable over said conductor between said spaced portions thereof.

2. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein, said groove being square in cross section; a second body having a disc with helical male screw threads disposed in said groove, said second body having a cylindrical passageway along its length, the axis of said passageway forming a helix of a diameter less than that of said groove and of a pitch greater than that of said groove, the surface defining said passageway being made of a low bearing friction insulating material; a conductive wire having a circular cross section, said wire having one end fixed to said first body at one end thereof, extending in said groove on one side of said second body toward said second body, extending through said second body passageway, and extending into said groove on the other side of said second body, the other end of said wire being fixed to said first body at the other end thereof, said one end of said first body containing a portion of said groove which has a surface made of a conductive material, the other end of said first body containing a portion of said groove which has a surface made of'an insulating material; and means to rotate said second body disc in said first body groove, said means including disc means at each end of said first body, a shaft means extending through said second body and rotatable in said disc means, and means on said shaft means and said disc means to cause rotation of said second body in said first body, said second body being axially slidable on said shaft means, said conductive wire being made of a spring metal, said conductive wire helix having an unstressed diameter greater than the diameter of said first body groove, said conductive wire thereby being maintained in tension in said first body groove.

3. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein; a second body having helical male screw threads disposed in said groove, said second body having a passageway along its length, the axis of said passageway forming a helix; a conductive wire having one end fixed to said first body at one end thereof, extending in said groove on one side of said second body toward said second body, extending through said second body passageway, and extending into said groove on the other side of said second body, the other end of said wire being fixed to said first body at the other end thereof, said first body groove having a conductive surface contiguous to only a portion of said conductive wire, at least a portion of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said first body groove.

4. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein; a sec- 6 ond body having helical male screw'threads disposed in said groove, said second body having a passageway along its length, the axis of said passageway forming a helix; a conductive wire having one end extending in said groove on one side of said second body toward said second body, extending through said second body passageway, and extending into said groove on the other side of said second body, said first body groove having a conductive surface contiguous to only a portion of said conductive wire, at least a portion of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said first body groove.

5. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein, said groove being square in cross section; a second body having helical male screw threads disposed in said groove, said second body having a passageway along its length, the axis of said passageway forming a helix; a conductive wire having a circular cross section, said wire having one end extending in said groove on one side of said second body toward said second body, extending through said second body passageway, and extending into said groove on the other side of said second body, said first body groove having a conductive surface contiguous to only a portion of said conductive wire, at least a portion of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said first body groove.

6. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein; a second body having helical male screw threads disposed in said groove, said second body having a passageway along its length, the axis of said passageway forming a helix of a diameter less than that of said groove and of a pitch greater than that of said groove; a conductive wire having one end extending in said groove on one side of said second body toward said second body, extending through said second body passageway, and extending into said groove on the other side of said second body, said first body groove having a conductive surface contiguous to only a portion of said conductive wire, at least a portion of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said first body groove.

7. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein; a second body having helical male screw threads disposed in said groove, said second body having a passageway along its length, the axis of said passageway forming a helix; a conductive wire having one end extending in said groove on one side of said second body toward said second body, extending through said second body passageway, and extending into said groove on the other side of said second body, said first body groove having a conductive surface contiguous to only a portion of said con-ductive wire, at least a portion of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said first body groove, said conductive wire being made of a spring metal, said conductive wire helix having an unstressed diameter greater than the diameter of said first body groove, said conductive wire thereby being maintained in tension in said first body groove.

8. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein, said groove being square in cross section; a second body having helical male screw threads disposed in said groove, said second body having a passageway along its length, the axis of said passageway forming a helix of a diameter less than that of said groove and of a pitch greater than that of said groove; a conductive wire having a circular cross section, said wire having one end extending in said groove on one side of said second body toward said second body, extending through said second body passageway, and extending into said groove on the other side of said second body, said first body groove having a conductive surface contiguous to only a portion of said conductive wire, at least a portion of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said first body groove.

9. A variable impedance comprising: a first body having an approximately cylindrical hole therein, the surface defining said hole having a helical groove therein, said groove being square in cross section; a second body having helical male screw threads disposed in said groove, said second body having a passageway along its length, the axis of said passageway forming a helix; a conductive wire having a circular cross section, said wire having one end extending in said groove on one side of said second body toward said second body, extending through said second body passageway, and extending into said groove on the other side of said second body, said first body groove having a conductive surface contiguous to only a portion of said conductive wire, at least a portion of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said first body groove, said conductive wire being made of a spring metal, said conductive wire helix having an unstressed diameter greater than the diameter of said first body groove,-said conductive wire thereby being main tained in tension insaid first body groove.

10. A variable impedance comprising: a first body having an approximately cylindrical-hole therein, the surface defining said hole having a helical groove therein; a second body having helical'male screw threads disposed in said groove, said second body having a passageway along its length, the axis of said passageway forming a helix of a diameter less than that of said groove and of a pitch greater than that of said groove; a conductive wire having one end extending in said groove on one side of said second body toward said second body, extending through said second bodypassageway, and extending into said groove on the other side of said second body, said first body groove having a conductive surface contiguous to only a portion of said conductive wire, at least aporti'on of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said first body groove, saidconductive wire be ing made of a spring metal, said conductive wire helix having an unstressed diameter greater than the diameter of said first body groove, said conductive wirethereby being maintained in tension in said first" body groove.

11. A- variable impedance comprising: a first body having an approximately cylindrical hole' therein, the surface defining said hole having a helical groove therein, said groove being square in cross section; a second body hav-' ing helical male screw threads disposed in said groove, said second body having a passageway along its length, the axis ofsaidpassageway' forming a helix of a diameter less than that of said groove and of a pitch greater than that of said groove; a conductive wire having acircular cross section, said wire having one end extending in said groove on one side of said second body toward said sec ond body, extending through said second body passageway, and extending into said groove on the other side of said second body, said first body groove having a conductive-surface contiguous to only a portion of said conductive wire, at least a portion of the surface of said first body groove being made of an insulating material; and means to rotate said second body in said firstbody groove, said conductive wire being made of a spring metal, said conductive wire helix having an unstressed diameter greater than the diameter of saidfirst body groove, said' conductive wire thereby being maintained in tension in said first body groove.

References Cited by the Examiner UNITED STATES PATENTS 1,904,208 4/1933 Dow g 336-144 X 2,037,061 4/1936 Bliss 33615 2,175,554 10/1939 Bliss 336-l5 2,731,605 1/1956 Doelz 336-15 3,085,215 4/1963 Shepherd 3 36l5 ROBERT K. SCHAEFER, Primary Examiner.

D. JAMES B'ADER, Assistant Examiner. 

3. A VARIABLE IMPEDANCE COMPRISING: A FIRST BODY HAVING AN APPROXIMATELY CYLINDRICAL HOLE THEREIN; FACE DEFINING SAID HOLE HAVING A HELICAL GROOVE THEREIN; A SECOND BODY HAVING HELICAL MALE SCREW THREADS DISPOSED IN SAID GROOVE, SAID SECOND BODY HAVING A PASSAGEWAY ALONG ITS LENGTH, THE AXIS OF SAID PASSAGEWAY FORMING A HELIX; A CONDUCTIVE WIRE HAVING ONE END FIXED TO SAID FIRST BODY AT ONE END THEREOF, EXTENDING IN SAID GROOVE ON ONE SIDE OF SAID SECOND BODY TOWARD SAID SECOND BODY, EXTENDING THROUGH SAID SECOND BODY PASSAGEWAY, AND EXTENDING INTO SAID GROOVE ON THE OTHER SIDE OF SAID SECOND BODY, THE OTHER END OF SAID WIRE BEING FIXED TO SAID FIRST BODY AT THE OTHER END THEREOF, SAID FIRST BODY GROOVE HAVING A CONDUCTIVE WIRE, AT LEAST A PORTION OF THE SURFACE OF SAID CONDUTIVE WIRE, AT LEAST A PORTION OF THE SURFACE OF SAID FIRST BODY GROOVE BEING MADE OF AN INSULATING MATERIAL; AND MEANS TO ROTATE SAID SECOND BODY IN SAID FIRST BODY GROOVE. 